Help out your poor neighbours. Help them achieve the same living standards etc that you have. They won't want to come no more illegal immigrants. Its a novel policy but you never know it might work. Cancel Foreign debt that might be a start. Start talking to Fidel you might help that nation out and learn a thing or two. Better living conditions in Cuba, fewer immigrants I would imagine. Like wise Mexico etc.
By the way help doesn't mean deciding what type of Gvt they should have and then imposing that upon them by military force blowing the Sh*t out of the place in order to achieve it, or supporting military juntas favourable to you, like in Chile, Bolivia, Nicaragua, El Salvador, Argentina etc, who then trample onthe rights of the people and set up dictatorships !